I just bought this '74 2.0, and started investigating things. I quickly discovered that the wheel hubs have studs, and they are screwed in, and not pressed in. Previous owner was using 911 lugs on these.
Is this common? Is it safe?

yes and yes.
make sure they used red loctite on the threads

And are the 911 lug nuts ok to use? Proper shape?

As long as the wheels are compatible with the lug nuts. Should be ball.

The studs are common-ish, but I am not a fan. My first 914 had them, and when I finally got around to looking at them I was not happy with the little amount they thread in.

--DD

I agree...and these were not in tight. I could unscrew most of them with a bare hand.

The red lock tight just keeps them from turning while you install the wheel/lugnuts. When you tighten the lug nuts, the threaded studs become secure as well. The nuts unscrew by hand until they are tightened down.

I've seen, sold and installed many of these during my first 20+ year career in tires. But like Dave, I'm not a fan of them. I normally prefer original style lug bolts, although I can see the advantage on the rear of a 914 where there is no hub-centering effect.

I will say that in all those years, I never saw any come loose or cause problems, assuming normal care during installation.

I'd rather have screw in studs with nuts than the bolts myself.

The studs used on the billet hubs are BBS racing studs similar to the 14mm ones below.

https://www.turnermotorsport.com/c-146-whee...-studs-and-nuts